1. The soteriological-trinitarian identity of each local Church and the more or less marked sociocultural plurality of them pose the problem of how this identity that constitutes their unity and communion can be recognized and become manifest in and through this plurality.
As fundamental criteria to recognize the identity may serve those elements which are repeatedly mentioned in the ecumenical debate as a prerequisite for the separated Churches to rediscover the lost unity:
- the fundamental faith of the Church as witnessed in the liturgy, in creeds or other common statements and finding a certain expression in the practical life of the baptized;
- the liturgy of the Church, especially the Eucharist structured around its poles Word and Sacrament;
- the ministry of the Church, especially the episkopé in its structural unfolding and integration in both the local Church and the communion of local Churches.
All these elements must show a sufficient degree of commonality which is an indication of the „theological“ identity of the local Churches. To recognize and preserve what is common in all plurality, to make a difference between essentials and other elements, is a constant task of the local Church and the communion of local Churches. Again, it cannot be fulfilled from a neutral point of view, but only by way of a common discernment that verges on a decision of faith. These elements will usually have a greater degree of uniformity within a local Church or a national Church than in a communion of Churches transcending these circumscriptions.
2. The Old Catholic belief of the Church is not articulated in a specific document but rather referred to as the Declaration of Utrecht points to the faith of the Ancient Church and to certain texts that serve as common elements of reference (like Holy Scripture, the creeds or dogmatic decisions of ecumenical synods). Formal declarations issued by the IBC (and received by the Church) will enjoy the status of authoritative clarifications in matters of belief. Other important statements showing common opinions in the Union of Utrecht may stem from institutions like the International Old Catholic Congress (since 1890, now meeting every four years) or the International Old Catholic Theological Conference (since 1950, usually meeting every year).
Apart from the liturgy of ordination  the liturgical formularies are the concern of the particular Churches. The integration in the „Western“ liturgical traditions and the modern liturgical renewal, however, guarantee a considerable degree of homogeneity. 
The ministry is perceived as identical in all the member Churches of the Union, although a closer analysis would probably reveal differences in the self-understanding of the clergy and in their social status.
Canon law as another possible common element in the member Churches differs very much in the degree of its elaboration.
So it may be said in conclusion that there is a relatively large scope for diversity in the Churches constituting the Union of Utrtecht.
3. A similar scope for diversity is explicitly provided for in the Anglican – Old Catholic Bonn Agreement of 1931: „Intercommunion does not require from either communion the acceptance of all doctrinal opinion, sacramental devotion, or liturgical practice characteristic of the other, but implies that each believes the other to hold all the essentials of the Christian faith“. The concluding text of the Orthodox-Old Catholic dialogue (1975-1987) says: „The consequence and expression of reciprocally recognized fellowship in the faith is the full liturgical-canonical communion of Churches, the realization of organic unity in the one Body of Christ. The liturgical and canonical consequences, which result from ecclesial fellowship, will be elucidated and regulated by the Church on the basis of the tradition of the undivided Church. This fellowship does not signify uniformity in liturgical order and ecclesial practice, but rather embodies an expression of the fact that the historically legitimated development of the one faith of the ancient and undivided Church is preserved in each of the participating Churches. This fellowship also does not require the subjection of one Church with its tradition to the other Church, for this would contradict the reality of the fellowship.“ It would be highly interesting, even ground-breaking, to see this task put into concrete action, but for various reasons this is not the case.
 The first common rite for the ordination of bishops, priestes, deacons (and minor orders, now suppressed) was published in 1897/99. The IBC approved of a revised rite in 1985 which was prepared by the International Old Catholic Liturgical Commission (appointed in 1978). It does not seem to be used in all the member Churches.
 Cf. the Consensus of the International Old Catholic Theological Conference of 1979 on the structure and the theology of the eucharistic prayer, IKZ 70 (1980) 226-229.
 Cf. Koinonia: 228.